Pressure-sensitive adhesive composition

ABSTRACT

Provided are a pressure-sensitive adhesive composition, a protective film, an optical device, and a display device. The pressure-sensitive adhesive composition may exhibit excellent storage stability, suitable low speed and high speed peel-off strengths after forming a crosslinking structure, and have an excellent balance between them. Accordingly, the pressure-sensitive adhesive composition may exhibit an excellent protective effect when applied to a protective film, may be easily peeled in a high speed peel-off and thus advantageous for a high speed process, and may exhibit an excellent antistatic characteristic.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International ApplicationNo. PCT/KR2014/005446, filed on Jun. 19, 2014, which claims priorityfrom Korean Patent Application No. 10-2013-0070512, filed on Jun. 19,2013, Korean Patent Application No. 10-2013-0070504, filed Jun. 19, 2013and Korean Patent Application No. 10-2013-0158649, filed Dec. 18, 2013,in the Korean Intellectual Property Office, the disclosures thereof areincorporated herein by reference.

FIELD

The present application relates to a pressure-sensitive adhesivecomposition, a film for protecting an optical device, an optical device,and a display device.

BACKGROUND

A protective film may be used to prevent adhesion of contaminants suchas dust and scratches on optical devices such as a polarizing plate,various plastic products, electric products, or automobiles. Suitablepeel-off strength and antistatic property may be required for theprotective film.

For example, when the protective film is peeled at a high speed in orderto use a product or assemble another product, a relatively low peel-offstrength (hereinafter, referred to as a “high speed peel-off strength”)is required. However, when the protective film is peeled at a low speed,the protective film may exhibit a suitable protecting function with arelatively high peel-off strength (hereinafter, referred to as a “lowspeed peel-off strength”).

In addition, due to static electricity generated in peeling of theprotective film, contaminants such as dust may be sucked, destruction ofstatic electricity of a device, if it is an electronic product, ormalfunction of the device may occur. Particularly, recently, ascomponents are integrated due to supply of a computer, andmultifunctionalization of a liquid crystal TV or a mobile phone,problems caused by static electricity may be being further magnified.

Accordingly, there is an attempt to provide an antistatic function to apressure-sensitive adhesive included in the protective film.

For example, there is an attempt to inhibiting generation of staticelectricity by adding an ethyleneoxide-modified phthalic acid dioctylplasticizer to a pressure-sensitive adhesive in the patent document 1.In addition, in the patent document 2, an organic salt is mixed to apressure-sensitive adhesive, and in the patent document 3, a metal saltand a chelating agent are mixed to a pressure-sensitive adhesive.However, according to the above-methods, contamination caused bytransfer of a pressure-sensitive adhesive component to a product to beprotected occurs, inhibition of static electricity generated in an earlystage is difficult, and a low speed peel-off strength critical to obtaina protective function is excessively reduced.

PRIOR ART DOCUMENTS Patent Documents

PATENT DOCUMENT 1: Japanese Laid-open Patent Application No. 1993-140519

PATENT DOCUMENT 2: Korean Unexamined Patent Application Publication No.2004-0030919

PATENT DOCUMENT 3: Korean Unexamined Patent Application Publication No.2006-0128659

DESCRIPTION Object

The present application provides a pressure-sensitive adhesivecomposition, a film for protecting an optical device, an optical device,and a display device.

Solution

In one aspect, the present application provides a pressure-sensitiveadhesive composition, which may include a polymer and an ionic compound.The polymer may include a polymerization unit of a monomer including analkyleneoxide chain, a polymerization unit of a nitrogen-containingmonomer, and a polymerization unit of a hydroxyl group-containingmonomer to exhibit suitable pressure-sensitive adhesive performance,antistatic performance, and peel-off characteristic. The term “monomer”used herein may refer to all types of compounds that can form a polymerthrough a polymerization reaction, and “the polymerization unit of amonomer” refers to a state in which a monomer is polymerized andincluded in a backbone of a side chain or a main chain of a polymer. Inaddition, unless particularly defined otherwise, the expression “apolymer includes, contains, or has a monomer” may mean that the monomeris included, contained, or had as a polymerization unit.

As a monomer having an alkyleneoxide chain, a compound represented byFormula 1 may be used:

In Formula 1, Q is hydrogen or an alkyl group, U is an alkylene group, Zis hydrogen, an alkyl group, or an aryl group, m is an optional number,for example, a number of 1 to 20.

In Formula 1, when at least two of the [—U—O—] units are present, thenumber of carbon atoms of U in each unit may be the same as ordifferent.

In Formula 1, m is, for example, a number in a range from 1 to 16, 1 to12, or 1 to 9. In such a range, polymerization efficiency andcrystallinity of a polymer in the preparation of the polymer may bemaintained in a suitable range, and suitable conductivity may beprovided to a pressure-sensitive adhesive.

The term “alkyl group” used herein may be, unless particularly definedotherwise, an alkyl group having 1 to 20, 1 to 16, 1 to 12, 1 to 8, or 1to 4 carbon atoms. The alkyl group may be linear, branched, or cyclic.The alkyl group maybe unsubstituted, or substituted by at least onesubstituent.

The term “alkylene or alkylidene group” used herein may be, unlessparticularly defined otherwise, an alkylene group or an alkylidene grouphaving 1 to 20, 1 to 16, 1 to 12, 1 to 8, or 1 to 4 carbon atoms. Thealkylene group or alkylidene group may be linear, branched, or cyclic.The alkylene group or alkylidene group may be substituted by at leastone substituent when needed.

In another embodiment, in Formula 1, Q is an alkyl group, for example,an alkyl group having 1 to 8 or 1 to 4 carbon atoms. When a compound inwhich Q is an alkyl group is used, for example, a pressure-sensitiveadhesive composition is applied to a protective film, and it can beadvantageous in that the protective film is easily removed without aresidue or stains on an adherend.

The “aryl group” used herein may be, unless particularly definedotherwise, a monovalent residue derived from a compound including astructure in which a benzene ring is included, or at least two benzenerings are connected, or at least two benzene rings are condensed orbound to each other with sharing one or at least two carbon atoms, or aderivative thereof. The aryl group may be, for example, an aryl grouphaving 6 to 25, 6 to 22, 6 to 16, or 6 to 13 carbon atoms. The arylgroup may be a phenyl group, a phenylethyl group, a phenylpropyl group,a benzyl group, a tolyl group, a xylyl group, or a naphthyl group.

In the specification, a specific functional group, for example, asubstituent that can be substituted to the alkyl group, the alkylidenegroup, or the alkylene group, may be, but is not limited to, an alkylgroup, an alkoxy group, an alkenyl group, an epoxy group, a cyano group,a carboxyl group, an acryloyl group, a methacryloyl group, anacryloyloxy group, a methacryloyloxy group, or an aryl group.

The compound of Formula 1 may be, but is not limited to, one or at leasttwo of alkoxy dialkyleneglycol (meth)acrylic acid ester, alkoxytrialkyleneglycol (meth)acrylic acid ester, alkoxy tetraalkyleneglycol(meth)acrylic acid ester, aryloxy dialkyleneglycol (meth)acrylic acidester, aryloxy trialkyleneglycol (meth)acrylic acid ester, aryloxytetraalkyleneglycol (meth)acrylic acid ester, and polyalkyleneglycolmonoalkyl ether (meth)acrylic acid ester.

Here, the alkoxy group may be, for example, an alkoxy having 1 to 20, 1to 16, 1 to 12, or 1 to 4 carbon atoms, and specifically, a methoxygroup or an ethoxy group.

Here, the alkyleneglycol may be an alkyleneglycol having 1 to 20, 1 to16, 1 to 12, or 1 to 4 carbon atoms, for example, ethyleneglycol orpropyleneglycol, and the aryloxy may be an aryloxy having 6 to 24 or 6to 12 carbon atoms, for example, phenoxy.

A type of the nitrogen-containing monomer included in the polymer maybe, but is not particularly limited to, for example, a monomercontaining an amide group, an amino group, an imide group, or a cyanogroup. Here, the monomer containing an amide group may be, for example,(meth)acrylamide or N,N-dimethyl (meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl (meth)acrylamide, N-methylol(meth)acrylamide, diacetone (meth)acrylamide, N-vinylacetoamide,N,N′-methylene bis(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N,N-dimethylaminopropyl methacrylamide,N-vinylpyrrolidone, N-vinylcaprolactam, or (meth)acryloylmorpholine, themonomer containing an amino group may be aminoethyl (meth)acrylate,N,N-dimethylaminoethyl (meth)acrylate, or N,N-dimethylaminopropyl(meth)acrylate, the monomer containing an imide group may beN-isopropylmaleimide, N-cyclohexylmaleimide, or itaconimide, and themonomer containing a cyano group may be acrylonitrile ormethacrylonitrile, but the present application is not limited thereto.To ensure suitable physical properties, for example, conductivity, andan excellent peel-off characteristic, for example, a balance between lowspeed and high speed peel-off strengths, particularly N,N-dialkyl(meth)acrylamide may be used as the nitrogen-containing monomer. In sucha case, the N,N-dialkyl (meth)acrylamide may include an alkyl grouphaving 1 to 20, 1 to 16, 1 to 12, 1 to 8, or 1 to 4 carbon atoms.

The polymer may further include a polymerization unit of the monomercontaining a hydroxyl group. The monomer may provide a hydroxyl group tothe polymer.

The monomer containing a hydroxyl group may be, for example, a monomerrepresented by Formula 2:

In Formula 2, Q is hydrogen or an alkyl group, A and B may be eachindependently an alkylene group, and n is an optional number, forexample, a number of 0 to 10.

In Formula 2, when at least two [—O—B—] units are present, the number ofcarbon atoms of B in each unit may be the same as or different.

In Formula 2, A and B may be, for example, each independently, a linearalkylene group.

The compound of Formula 2 may be, but is not limited to, 2-hydroxyethyl(meth)acrylate, 2-hydroypropyl (meth)acrylate, 4-hydroxybutyl(meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl(meth)acrylate, 2-hydroxyethyleneglycol (meth)acrylate, or2-hydroxypropyleneglycol (meth)acrylate.

In one embodiment, as the monomer containing a hydroxyl group, two typesof monomers, which have different numbers of carbon atoms at side chainsmay be used.

For example, the polymer may include a polymerization unit of a firstmonomer in which each of alkylene groups at A and B of Formula 2 has 1to 3 carbon atoms, and a polymerization unit of a second monomer inwhich each of alkylene groups at A and B of Formula 2 has 4 to 20, 4 to16, 4 to 12, 4 to 8, or 4 to 6 carbon atoms.

To distinguish the first and second monomers, when the number of carbonatoms are calculated, only the number of carbon atoms of a linearalkylene group is considered, and therefore, for example, when acarbon-containing substituent is substituted to A and B, the number ofcarbon atoms of the substituent is not considered. As a result, due tothe polymerization units of the two types of the monomers containing ahydroxyl group, a pressure-sensitive adhesive may exhibit an excellentpeel-off characteristic, that is, an excellent balance between highspeed and low speed peel-off strengths.

To ensure an optimal range of all physical properties including apressure-sensitive adhesive performance, and a peel-off characteristic,that is, an excellent balance between low speed and high speed peel-offstrengths, the weight ratio of the first and second monomers in thepolymer may be controlled. For example, the ratio (A/B) of the weight(A) of the first monomer and the weight (B) of the second monomer in thepolymer may be more than 1. In another embodiment, the ratio may beapproximately 1.1 or more or 1.2 or more. In another embodiment, theratio may also be 25 or less, 20 or less, 15 or less, 10 or less, orapproximately 8 or less. Therefore, in such a range, thepressure-sensitive adhesive exhibiting a suitable antistatic performanceand a suitable balance between high speed and low speed peel-offstrengths without leaving contaminants during peeling may be provided.

The polymer may include a polymerization unit of 0.1 to 6.0 parts byweight of the monomer of Formula 1, a polymerization unit of 1 to 30parts by weight of the nitrogen-containing monomer, a polymerizationunit of 0.1 to 15 parts by weight of the first monomer, and apolymerization unit of 0.1 to 5 parts by weight of the second monomer.Unless particularly defined otherwise, the unit “parts by weight” usedherein may mean a weight ratio between components. For example, theexpression “the polymer includes a polymerization unit of 0.1 to 6.0parts by weight of the monomer of Formula 1, a polymerization unit of 1to 30 parts by weight of the nitrogen-containing monomer, apolymerization unit of 0.1 to 15 parts by weight of the first monomer,and a polymerization unit of 0.1 to 5 parts by weight of the secondmonomer” as mentioned above means that the polymer is formed from amonomer mixture including the weight (A) of the monomer of Formula 1,the weight (B) of the nitrogen-containing monomer, the weight (C) of thefirst monomer, and the weight (D) of the second monomer in a ratio(A:B:C:D) of 0.1 to 6:1 to 30:0.1 to 15:0.1 to 5. In another embodiment,the polymer may include a polymerization unit of 0.5 to 6 or 1 to 6parts by weight of the monomer of Formula 1. The polymer may include apolymerization unit of 1 to 25, 1 to 20, 1 to 13, or 2 to 13 parts byweight of the nitrogen-containing monomer. In still another embodiment,the polymer may include a polymerization unit of approximately 1 to 15parts by weight of the first monomer, and a polymerization unit ofapproximately 1 o 3 parts by weight of the second monomer In thepolymer, a weight ratio (E) of the monomer of Formula 1 and a weightratio (N) of the nitrogen-containing monomer may be additionallycontrolled, and the weight ratio (N/E) may be controlled in a range of,for example, approximately 0.1 to 10, 0.1 to 9, 0.1 to 8, 0.1 to 7, or0.1 to 6.

The polymer may further include a polymerization unit of a (meth)acrylicacid ester monomer, for example, an alkyl (meth)acrylate.

As the alkyl (meth)acrylate, for example, in consideration of a cohesivestrength, glass transition temperature, or pressure-sensitive adhesiveproperty of a pressure-sensitive adhesive, an alkyl (meth)acrylatehaving an alkyl group having 1 to 14 carbon atoms may be used. Such amonomer may be methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl(meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate,t-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate,2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, n-octyl(meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl(meth)acrylate, or tetradecyl (meth)acrylate, and one or at least twothereof maybe included in the polymer as a polymerization unit.

The polymer may include a polymerization unit of 65 to 99 or 70 to 90parts by weight of a (meth)acrylic acid ester monomer. The weight ratiomay be changed in consideration of, for example, a specific type of eachmonomer when needed.

The polymer may further include a known monomer used in preparation of apolymer of a pressure-sensitive adhesive, for example, a carboxylgroup-containing monomer such as (meth)acrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth)acryloyloxy propylic acid, 4-(meth)acryloyloxybutyric acid, acrylic acid dimer, itaconic acid, maleic acid, or maleicanhydride; a monomer having an isocyanate group; a monomer having aglycidyl group such as glycidyl (meth)acrylate; a radical polymerizablemonomer including a nitrogen atom such as (meth)acrylamide, N-vinylpyrrolidone, or N-vinyl caprolactam; or a radical polymerizable monomersuch as styrene when needed. Such monomers are polymerized and includedin the polymer, and may be included in the polymer, for example, atapproximately 20 parts by weight or less.

The polymer may be prepared by selecting a suitable monomer from theabove-described monomers, and applying a mixture of the selectedmonomers in a desired ratio to a polymerization method such as solutionpolymerization, photo polymerization, bulk polymerization, suspensionpolymerization, or emulsion polymerization.

The pressure-sensitive adhesive composition may include aphotostabilizer such as a hindered amine compound. Since such aphotostabilizer is not cohered even when a pressure-sensitive adhesiveis maintained at a high temperature, it does not cause a phenomenon ofincreasing a concentration of an antistatic agent which will bedescribed below in a cohesive cluster, prevents generation of radicalsby breaking an ether bond part of an alkyleneoxide chain included in thepolymer or condensation of the hydroxyl group-containing monomer, andcan greatly improve storage stability of the pressure-sensitive adhesivecomposition.

The photostabilizer may be, for example, a compound represented byFormula 3.

In Formula 3, M₁ to M₅ are each independently R¹—N, (R²)(R³)—C, or(R⁴)(R⁵)—C, in which R¹ is a hydrogen atom, an alkyl group, or an alkoxygroup, R² and R³ are each independently an alkyl group, R⁴ and R⁵ areeach independently a hydrogen atom or an alkyl group, L is an alkylenegroup or an alkylidene group, P is an alkyl group or a substituent ofFormula 4. In Formula 3, at least one of M₂ to M₄ is R¹—N, and M₁, M₂,M₃, M₄, or M₅ just adjacent to M₂, M₃, or M₄ that is R¹—N may be(R²)(R³)—C.

In Formula 4, M₆ to M₁₀ are each independently R¹—N, (R²)(R³)—C, or(R⁴)(R⁵)—C, in which R¹ is a hydrogen atom, an alkyl group, or an alkoxygroup, R² and R³ are each independently an alkyl group, and R⁴ and R⁵are each independently a hydrogen atom or an alkyl group. In Formula 4,at least one of M₇ to M₉ is R¹—N, and M₆, M₇, M₈, M₉, or M₁₀ justadjacent to M₇, M₈, or M₉ that is R¹—N may be (R²)(R³)—C.

In Formulas 3 and 4, the expression “M₁ to M₁₀ are R¹—N, (R²)(R³)—C, or(R⁴)(R⁵)—C” may mean that a nitrogen (N) atom or a carbon (C) atom ispresent at the position of M₁ to M₁₀, and a substituent selected from R¹to R⁵ binds to the nitrogen atom or the carbon atom.

In addition, in Formula 4, the mark

means that the carbon atom of Formula 4 linked to the mark binds to theoxygen atom of Formula 3.

In Formula 3, the alkylene group or alkylidene group, that is, L, may besubstituted or non-substituted when needed. For example, L may besubstituted by an aryl group, which may be, but is not limited to, a3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl group.

In Formula 3, R¹ may be, for example, a hydrogen atom, an alkyl grouphaving 1 to 8 or 1 to 4 carbon atoms, or an alkoxy group having 4 to 16or 4 to 12 carbon atoms. The alkyl group or the alkoxy group may belinear or branched, and may be substituted by at least one substituent.

In Formula 3, R², R³, and P may be each independently an alkyl grouphaving 1 to 12, 1 to 8, or 1 to 4 carbon atoms. The alkyl group may belinear or branched, and may be substituted by at least one substituent.

In addition, in Formula 3, R⁴ and R⁵ may be hydrogen atoms.

In addition, in Formula 3, L may be, for example, an alkylene grouphaving 4 to 12 or 6 to 10 carbon atoms, or an alkylidene group having 2to 10 or 4 to 8 carbon atoms. The alkylene group or alkylidene group maybe linear or branched, and may be substituted by at least onesubstituent.

The compound of Formula 3 may be, but is not limited to, for example,bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, methyl1,2,2,6,6-pentamethyl-4-piperidyl sebacate, propanedioic acid2-[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]-2-butyl-1,3-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)ester, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, orbis-(1-octyloxy-2,2,6,6-tetramethyl-4-piperidinyl)sebacate.

The compound of Formula 3 may be included in the pressure-sensitiveadhesive composition at 0.01 to 10, 0.05 to 10, 0.05 to 8, 0.05 to 6, or0.05 to 5 parts by weight relative to 100 parts by weight of thepolymer. In such a range, a pressure-sensitive adhesive compositionwhich effectively prevents generation of radicals by breakage of thealkyleneoxide chain or condensation of a hydroxyl group-containingmonomer, and has excellent storage stability may be provided.

The pressure-sensitive adhesive composition may further include acrosslinking agent, and implement a crosslinking structure by a reactionwith a crosslinking point of the polymer.

For example, as the crosslinking agent, an aliphatic isocyanatecrosslinking agent may be used. When such a crosslinking agent forms acrosslinking structure with the polymer, that is, a polymer including atleast two hydroxyl group-containing monomers, a pressure-sensitiveadhesive having suitable low speed and high speed peel-off strengths anda necessary antistatic characteristic may be implemented. For example,as the crosslinking agent, a crosslinking agent including an aliphaticcyclic isocyanate compound and/or an aliphatic non-cyclic isocyanatecompound may be used. Here, the term “aliphatic cyclic isocyanatecompound” may refer to an isocyanate compound including a cyclicstructure, which does not correspond to an aromatic ring, and the“aliphatic non-cyclic isocyanate compound” may refer to, for example, analiphatic linear or branched isocyanate compound. Here, the aliphaticcyclic isocyanate compound may be, for example, an isocyanate compoundsuch as isophorone diisocyanate, methylene dicyclohexyl diisocyanate, orcyclohexane diisocyanate, a derivative such as a dimer or trimerthereof, or a reaction product of any one of the above compounds with apolyol (e.g., trimethylolpropane), and the aliphatic non-cyclicisocyanate compound may be an alkylene diisocyanate compound having 1 to20, 1 to 16, 1 to 12, or 1 to 8 carbon atoms such as hexamethylenediisocyanate, a derivative such as a dimer or trimer thereof, or areaction product of any one of the above compounds with a polyol (e.g.,trimethylolpropane), but the present application is not limited thereto.

Here, when the aliphatic cyclic isocyanate compound and the aliphaticnon-cyclic isocyanate compound are used together, the ratios are notparticularly limited, and may be appropriately selected according tonecessity. Conventionally, the crosslinking agent may includeapproximately 1 to 500 or 20 to 300 parts by weight of the aliphaticnon-cyclic isocyanate compound relative to 100 parts by weight of thealiphatic cyclic isocyanate compound. As the crosslinking agent, thatis, as the crosslinking agent including an aliphatic cyclic isocyanatecompound and an aliphatic non-cyclic isocyanate compound, commerciallyavailable one, for example, MHG-80B and Duranate P produced by Asahi orNZ-1 produced by BAYER may be used.

When additionally needed, a known crosslinking agent such as an epoxycrosslinking agent such as ethyleneglycol diglycidylether,triglycidylether, trimethylolpropane triglycidylether,N,N,N′,N′-tetraglycidyl ethylenediamine, or glycerin diglycidylether; anaziridine crosslinking agent such as N,N′-toluene-2,4-bis(1-aziridinecarboxamide), N,N′-diphenylmethane-4,4′-bis(1-aziridine carboxamide),triethylenemelamine, bis isoprothaloyl-1-(2-methylaziridine), ortri-1-aziridinyl phosphineoxide; or a metal chelate crosslinking agentsuch as a compound prepared by coordinating a multifunctional metal suchas aluminum, iron, zinc, tin, titanium, antimony, magnesium, and/orvanadium to acetyl acetone or ethyl acetoacetate may also be used.

The pressure-sensitive adhesive composition may include a crosslinkingagent at 0.01 to 10 or 0.01 to 5 parts by weight relative to 100 partsby weight of the polymer. In such a range, a suitable crosslinkingstructure may be implemented, and the low speed and high speed peel-offstrengths of the pressure-sensitive adhesive may be controlled in adesired range.

The pressure-sensitive adhesive composition may further include anantistatic agent. As the antistatic agent, for example, an ioniccompound may be used.

As the ionic compound, for example, a meal salt may be used. The metalsalt may include, for example, an alkali metal cation or an alkali earthmetal cation. The cation may be one or at least two of a lithium ion(Li⁺), a sodium ion (Na⁺), a potassium ion (K⁺), a rubidium ion (Rb⁺), acesium ion (Cs⁺), a beryllium ion (Be²⁺), a magnesium ion (Mg²⁺), acalcium ion (Ca²⁺), a strontium ion (Sr²⁺), and a barium ion (Ba²⁺),preferably, one or at least two of a lithium ion, a sodium ion, apotassium ion, a magnesium ion, a calcium ion, and a barium ion, andmore preferably, a lithium ion in consideration of ion stability andmobility.

The anion included in the ionic compound may be PF₆ ^(−,) AsF⁻, NO₂ ⁻,fluoride (F⁻), chloride (Cl⁻), bromide (Br⁻), iodide (I⁻), perchlorate(CIO₄ ⁻), hydroxide (OH⁻), carbonate (CO₃ ²⁻), nitrate (NO₃ ⁻),trifluoromethanesulfonate (CF₃SO₃ ⁻), sulfonate (SO₄ ⁻),hexafluorophosphate (PF₆ ⁻), methylbenzenesulfonate (CH₃ (C₆H₄)SO₃ ⁻),p-toluenesulfonate (CH₃C₆H₄SO₃ ⁻), tetraborate (B₄O₇ ²⁻),carboxybenzenesulfonate (COOH(C₆H₄)SO₃ ⁻), trifluoromethanesulfonate(CF₃SO₂ ⁻), benzonate (C₆H₅COO⁻), acetate (CH₃COO⁻), trifluoroacetate(CF₃COO⁻), tetrafluoroborate (BF₄ ⁻), tetrabenzylborate (B(C₆H₅)₄ ⁻), ortrispentafluoroethyl trifluorophosphate (P(C₂F₅)₃F₃ ⁻).

In another embodiment, as the anion, the anion represented by Formula 5or bisfluorosulfonylimide may be used.[X(YO_(m)R_(f))_(n)]⁻  [Formula 5]

In Formula 5, X is a nitrogen atom or a carbon atom, Y is a carbon atomor a sulfur atom, R_(f) is a perfluoroalkyl group, m is 1 or 2, and n is2 or 3.

In Formula 5, when Y is carbon, m may be 1, when Y is sulfur, m may be2, when X is nitrogen, n may be 2, and when X is carbon, n may be 3.

The anion of Formula 5 or bis(fluorosulfonyl)imide exhibits a highelectronegativity due to a perfluoroalkyl (R_(f)) group or a fluorogroup, and includes a unique resonance structure, which forms a weakbond with a cation, thereby having hydrophobicity. Accordingly, theionic compound may exhibit excellent compatibility with anothercomponent of the composition such as a polymer, and may provide a highantistatic ability with a small amount.

The R_(f) of Formula 5 may be a perfluoroalkyl group having 1 to 20, 1to 12, 1 to 8, or 1 to 4 carbon atoms, and in this case, theperfluoroalkyl group may have a linear, branched, or cyclic structure.The anion of Formula 5 may be a sulfonylmethide-, sulfonylimide-,carbonylmethide-, or carbonylimide-based anion, and specifically, one ora mixture of at least two of tristrifluoromethanesulfonylmethide,bistrifluoromethanesulfonylimide, bisperfluorobutanesulfonylimide,bispentafluoroethanesulfonylimide, tristrifluoromethanec arbonylmethide,bisperfluorobutanecarbonylimide, and bispentafluoroethanecarbonylimide.

As the ionic compound, an organic salt including a quaternary ammoniumsuch as N-ethyl-N,N-dimethyl-N-propylammonium,N,N,N-trimethyl-N-propylammonium, N-methyl-N,N,N-tributylammonium,N-ethyl-N,N,N-tributylammonium, N-methyl-N,N,N-trihexylammonium,N-ethyl-N,N,N-trihexylammonium, N-methyl-N,N,N-trioctylammonium, orN-ethyl-N,N,N-trioctylammonium, phosphonium, pyridinium, imidazolium,pyrrolidinium, or piperidinium as a cation and the anionic component maybe used, and when needed, the metal salt may be used in combination withthe organic salt.

A content of the ionic compound in the pressure-sensitive adhesivecomposition may be approximately, but is not particularly limited to,for example, 0.01 to 5 parts by weight relative to 100 parts by weightof the polymer. The ratio of the ionic compound may be changed inconsideration of a desired antistatic property or compatibility betweencomponents.

The pressure-sensitive adhesive composition may further include a silanecoupling agent. The coupling agent may be γ-glycidoxypropyl triethoxysilane, γ-glycidoxypropyl trimethoxy silane, γ-glycidoxypropylmethyldiethoxy silane, γ-glycidoxypropyl triethoxy silane,3-mercaptopropyl trimethoxy silane, vinyltrimethoxy silane,vinyltriethoxy silane, γ-methacryloxypropyl trimethoxy silane,γ-methacryloxy propyl triethoxy silane, γ-aminopropyl trimethoxy silane,γ-aminpropyl triethoxy silane, 3-isocyanatopropyl triethoxy silane,γ-acetoacetatepropyl trimethoxy silane, γ-acetoacetatepropyl triethoxysilane, β-cyanoacetyl trimethoxy silane, β-cyanoacetyl triethoxy silane,or acetoxyacetotrimethoxy silane, which may be used alone or incombination of at least two thereof. For example, as the silane couplingagent, a silane coupling agent having an acetoacetate or β-cyanoacetylgroup is preferably used. In the pressure-sensitive adhesivecomposition, the silane coupling agent may be included at 0.01 to 5 or0.01 to 1 part by weight relative to 100 parts by weight of the polymer.In the above range, an appropriate increase in a pressure-sensitiveadhesive strength and durability and reliability may be ensured.

The pressure-sensitive adhesive composition may further include atackifier in an aspect of controlling a pressure-sensitive adhesiveperformance. The tackifier may be a hydrocarbon-based resin or ahydrogenated product thereof, a rosin resin or a hydrogenated productthereof, a rosin ester resin or a hydrogenated product thereof, aterpene resin or a hydrogenated product thereof, a terpene phenol resinor a hydrogenated product thereof, a polymerized rosin resin, or apolymerized rosin ester resin, which may be used alone or in combinationof at least two thereof. The tackifier may be included in thecomposition at 1 to 100 parts by weight relative to 100 parts by weightof the copolymer. In the content range, a suitable addition effect andenhancement in compatibility and a cohesive strength may be ensured.

The pressure-sensitive adhesive composition may further include at leastone additive selected from the group consisting of acoordinationcompound capable of forming a coordinate bond with theantistatic agent, a photoinitiator, a multifunctional acrylate, an epoxyresin, a crosslinking agent, a UV stabilizer, an antioxidant, a coloringagent, a reinforcing agent, a filler, a foaming agent, a surfactant, anda plasticizer as long as it does not affect the desired effect.

The pressure-sensitive adhesive composition may have a low speedpeel-off strength to an adherend having surface energy of 30 mN/m orless in a state in which a crosslinking structure is implemented ofapproximately 1 to 40, 1 to 30, 1 to 20, or 1 to 10 gf/25 mm, and a highspeed peel-off strength of approximately 10 to 300, 10 to 250, 10 to200, 10 to 150, or 10 to 100 gf/25 mm.

Here, the term “low speed peel-off strength” may be, for example, apeel-off strength measured at a peel-off angle of 180 degrees and apeel-off speed of 0.3 m/min, and the “high speed peel-off strength” maybe a peel-off strength measured at a peel-off angle of 180 degrees and apeel-off speed of 30 m/min.

Specifically, each of the peel-off strength may be measured at theabove-described peel-off angle and peel-off speed after thepressure-sensitive adhesive composition in which a crosslinkingstructure is implemented is adhered to an adherend having surface energyof 30 mN/m or less, maintained at a temperature of 23° C. and a relativehumidity of 65% for 24 hours. A specific method of measuring thepeel-off strength will be described in the following Example.

A method of measuring surface energy of the adherend may be a knownmethod of measuring surface energy, but the present application is notparticularly limited thereto. For example, the surface energy may becalculated by measuring a contact angle of the adherend, or may bemeasured using known surface energy measuring equipment. The surfaceenergy of the adherend may be approximately, for example, 10 to 30 mN/m.

The pressure-sensitive adhesive composition may also have a ratio (II/L)of the high speed peel-off strength (H) to the low speed peel-offstrength (L) of 1 to 30, 1 to 25, 1 to 20, 5 to 20, or 7 to 15.

The pressure-sensitive adhesive composition may have a peel-offelectrostatic discharge (ESD) generated when peeled from the adherend,that is, the adherend having surface energy of 30 mN/m or less at apeel-off angle of 180 degrees and a peel-off speed of 40 m/min in astate in which a crosslinking structure is implemented, of 0.7 kV orless. The method of measuring a peel-off ESD will be described in thefollowing Example.

When such low speed and high speed peel-off strengths and/or peel-offESD are ensured, the pressure-sensitive adhesive composition may exhibita suitable protective function to an adherend, may minimize occurrenceof static electricity, and may be easily peeled at a high speed.

In another aspect, the present application provides a pressure-sensitiveadhesive sheet. The pressure-sensitive adhesive sheet may be, forexample, a protective film, and particularly, a protective film for anoptical device.

For example, the pressure-sensitive adhesive sheet may be used as aprotective film for an optical device such as a polarizing plate, apolarizer, a polarizer protective film, a viewing angle compensationfilm, or a brightness enhancing film. The terms “polarizer” and“polarizing plate” used herein are objects different from each other.That is, the polarizer refers to a film, sheet, or device exhibiting apolarizing function, and the polarizing plate refers to an opticaldevice including another component in addition to the polarizer. Asanother factor that can be included in the optical device in addition tothe polarizer, a polarizer protective film or a retardation film may beused, but the present application is not limited thereto.

The pressure-sensitive adhesive sheet may include, for example, a basefilm for protecting a surface and a pressure-sensitive adhesive layerpresent on one surface of the base film. The pressure-sensitive adhesivelayer may include, for example, a crosslinked pressure-sensitiveadhesive composition, that is, a pressure-sensitive adhesive compositionin which a crosslinking structure is implemented, as thepressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition exhibits a relatively highlow speed peel-off strength and a relatively low high speed peel-offstrength after a crosslinking structure is implemented, excellentbalance between the peel-off strengths, and excellent durability andreliability, workability, transparency, and an antistatic property.Accordingly, the protective film may be effectively used as a surfaceprotective film to protect various types of optical devices or parts, ordisplay devices or parts, for example, a surface of an optical devicesuch as a polarizing plate, a retardation plate, an optical compensationfilm, a reflective sheet, and a brightness enhancing film used in anLCD, and the above uses are not limited to the protective film.

As the base film for protecting a surface, a general film or sheet knownin the art may be used. For example, the base film for protecting asurface may be a plastic film such as a polyester film formed ofpolyethyleneterephthalate or polybutyleneterephthalate, apolytetrafluoroethylene film, a polyethylene film, a polypropylene film,a polybutene film, a polybutadiene film, a poly(vinyl chloride) film, ora polyimide film. Such a film may be composed of a single layer, or astacked structure of at least two layers, and in some cases, furtherinclude a functional layer such as an antistaining layer or anantistatic layer. In addition, to enhance base cohesion, surfacetreatment such as primer treatment may be performed on one or bothsurfaces of the base.

A thickness of the base film is suitably selected according to a use,and may be conventionally, but is not particularly limited to, 5 to 500μm or 10 to 100 μm.

A thickness of the pressure-sensitive adhesive layer included in thepressure-sensitive adhesive sheet may be approximately, but is notparticularly limited to, for example, 2 to 100 μm or 5 to 50 μm.

A method of forming the pressure-sensitive adhesive layer may be, but isnot particularly limited to, for example, coating a pressure-sensitiveadhesive composition or a coating solution prepared thereof on a basefilm using a conventional means such as a bar coater and curing thecoated pressure-sensitive adhesive composition or coating solution, orcoating a pressure-sensitive adhesive composition or a coating solutionon a surface of a peelable base and curing the coated pressure-sensitiveadhesive composition or coating solution and then transferring thecoated pressure-sensitive adhesive composition or coating solution tothe base film.

A process of forming the pressure-sensitive adhesive layer may beperformed after a volatile component, or a bubbling component such as areaction residue in the pressure-sensitive adhesive composition orcoating solution is sufficiently removed. Accordingly, problems ofreducing an elastic modulus due to an excessively low crosslinkingdensity or a molecular weight of the pressure-sensitive adhesive, andforming a scatterer in the pressure-sensitive adhesive layer due toincreasing bubbles present between a glass plate and apressure-sensitive adhesive layer at a high temperature may beprevented.

In the above process, a method of curing the pressure-sensitive adhesivecomposition is not particularly limited, either, and may be performedthrough a suitable aging process that can react a polymer with acrosslinking agent included in the composition, or light radiation, forexample, UV radiation that can induce activation of a photoinitiatortherein.

The pressure-sensitive adhesive layer may have, for example, a gelcontent of approximately 80 to 99%. The gel content may be calculatedby, for example, Expression 1:Gel content=B/A×100  [Expression 1]

In Expression 1, A is a mass of the pressure-sensitive adhesive, and Bis a dry mass of an insoluble content recovered after thepressure-sensitive adhesive is dipped in ethyl acetate at roomtemperature for 48 hours.

In still another aspect, the present application provides an opticaldevice. The illustrative optical device may include an optical element,and the pressure-sensitive adhesive sheet adhered to a surface of theoptical element. For example, a pressure-sensitive adhesive layer of thepressure-sensitive adhesive sheet is adhered to a surface of the opticalelement, and therefore the optical element may be protected by the basefilm for protecting a surface.

The optical element included in the optical device may be, for example,a polarizer, a polarizing plate, a polarizer protective film, aretardation layer, or a viewing angle compensation layer.

Here, as the polarizer, for example, a general type known in the artsuch as a polyvinylalcohol polarizer may be employed without limitation.

The polarizer is a functional film or sheet that can extract only lightoscillating in one direction from incident light oscillating in variousdirections. Such a polarizer may be, for example, a form in which adichroic dye is adsorbed and oriented on a polyvinylalcohol-based resinfilm. The polyvinylalcohol-based resin constituting a polarizer may beobtained by, for example, gelating a polyvinylacetate-based resin. Inthis case, in the polyvinylacetate-based resin that can be used, inaddition to a homopolymer of vinyl acetate, a copolymer of vinyl acetateand a different monomer copolymerized therewith may be included. Here,an example of a monomer that can be copolymerized with vinyl acetate maybe, but is not limited to, one or a mixture of at least two ofunsaturated carbonic acids, olefins, vinyl ethers, unsaturated sulfonicacids, and acryl amides having an ammonium group. A degree of gelationof the polyvinyl alcohol-based resin may be approximately 85 to 100 mol%, and preferably 98 mol % or more. The polyvinyl alcohol-based resinmay be further modified, and for example, polyvinyl formal or polyvinylacetal modified by aldehydes may also be used. In addition, a degree ofpolymerization of the polyvinyl alcohol-based resin may be approximately1,000 to 10,000, and preferably 1,500 to 5,000.

A disc-shaped film of the polarizer may be formed using the polyvinylalcohol-based resin. A method of forming a film using a polyvinylalcohol-based resin may be, but is not particularly limited to, ageneral method known in the art. A thickness of the disc-shaped filmformed of the polyvinyl alcohol-based resin may be, but is notparticularly limited to, for example, suitably controlled within a rangeof 1 to 150 μm. In consideration of stretching feasibility, thethickness of the disc-shaped film may be controlled to 10 μm or more.The polarizer may be manufactured by a process of stretching (e.g.,uniaxial stretching) the polyvinyl alcohol-based resin film, a processof dying the polyvinyl alcohol-based resin film with a dichroic dye andadsorbing the dichroic dye, a process of treating the polyvinylalcohol-based resin film to which the dichroic dye is adsorbed with aboric acid aqueous solution, and a process of washing the polyvinylalcohol-based resin film after treated with the boric acid aqueoussolution. Here, as the dichroic dye, iodine or a dichroic organic dyemay be used.

The polarizing plate may include, for example, the polarizer; andanother optical film adhered to one or both surfaces of the polarizer.Here, as another optical film, the above-described polarizer protectivefilm, a retardation layer, a viewing angle compensation layer, or anantiglare layer may be used.

Here, the polarizer protective film may be a protective film to thepolarizer to be distinguished from the protective film including thepressure-sensitive adhesive layer. As the polarizer protective film, forexample, a multilayer film stacked with protective films composed of acellulose-based film such as triacetyl cellulose; an acryl film; apolyester-based film such as a polycarbonate film orpolyethyleneterephthalate film; a polyethersulfone-based film; and/or apolyolefin-based film such as a polyethylene film, a polypropylene film,a polyolefin film having a cyclic or norbornene structure, or anethylene propylene copolymer. A thickness of the protective film is notparticularly limited, either, and therefore the protective film may beformed to a conventional thickness.

A surface treatment layer may be present on a surface of the opticalelement protected by the protective film in the optical device. Thesurface treatment layer may have surface energy of, for example, 30 mN/mor less. That is, in the optical device, the surface treatment layerhaving surface energy of 30 mN/m or less may be formed on a surface ofthe optical element protected by the protective film, and thepressure-sensitive adhesive layer of the protective film may be adheredto the surface treatment layer.

The surface treatment layer may be a high hardness layer, an a glarinesspreventing layer such as an antiglare (AG) layer or a semi-glare (SG)layer, or a low reflection layer such as an anti-reflection (AR) layeror a low-reflection (LR) layer.

The high hardness layer may be a layer having a pencil hardness under aload of 500 g of 1H or more or 2H or more. The pencil hardness may bemeasured, for example, using a pencil lead regulated in KS G2603according to ASTM D 3363.

The high hardness layer may be, for example, a high-hardness resinlayer. The resin layer may include, for example, a roomtemperature-curable, moisture-curable, heat-curable, or active energyray-curable resin composition in a cured state. In one embodiment, theresin layer may include a heat-curable or active energy ray-curableresin composition, or an active energy ray-curable resin composition ina cured state. In the description of the high hardness layer, the “curedstate” may mean a state in which components included in each resincomposition are subjected to crosslinking or polymerization, andtherefore the resin composition is converted into a hard state. Inaddition, here, the room temperature-curable, moisture-curable,heat-curable, or active energy ray-curable resin composition may be acomposition which is cured at a room temperature, or cured byirradiation of heat or active energy rays under suitable humidity.

Various resin compositions that can satisfy a pencil hardness in theabove-described range in a cured state are known in the art, and one ofordinary skill in the art may easily select a suitable resincomposition.

In one embodiment, the resin composition may include an acryl compound,an epoxy compound, a urethane compound, a phenol compound, or apolyester compound as a main component. The “compound” may be amonomeric, oligomeric, or polymeric compound.

In one embodiment, the resin composition may be an acryl resincomposition having an excellent optical characteristic such astransparency and excellent resistance to yellowing, for example, anactive energy ray-curable acryl resin composition.

The active energy ray-curable acryl composition may include, forexample, an active energy ray-polymerizable polymer component and amonomer for reactive dilution.

The polymer component may be a component known in the art as an activeenergy ray-polymerizable oligomer such as urethane acrylate, epoxyacrylate, ether acrylate, or ester acrylate, or a polymer of a mixtureincluding a monomer such as a (meth)acrylic ester monomer. Here, the(meth)acrylic ester monomer may be an alkyl (meth)acrylate, a(meth)acrylate having an aromatic group, a heterocyclic (meth)acrylate,or alkoxy (meth)acrylate. Various polymer components to prepare anactive energy ray-curable composition are known in the art, and theabove-described compound may be selected according to necessity.

As the monomer for reactive dilution that can be included in the activeenergy ray-curable acryl composition may be a monomer having one or atleast two of an active energy ray-curable functional group, for example,an acryloyl group or a methacryloyl group. As the monomer for reactivedilution, for example, the (meth)acrylic acid ester monomer or amultifunctional acrylate may be used.

Selection of the component to prepare the active energy ray-curableacryl composition or a mixing ratio of the selected component is notparticularly limited, and may be controlled in consideration of ahardness and other physical properties of a desired resin layer.

As the glariness preventing layer such as an AG layer or an SG layer,for example, a resin layer having an uneven surface, or a resin layerincluding particles that have a different refractive index from that ofthe resin layer may be used.

Here, as the resin layer, for example, a resin layer used to form thehigh hardness layer may be used. When the glariness preventing layer isformed, it is not necessary to control components of a resin compositionfor the resin layer to have a high hardness, but a resin layer may beformed to exhibit a high hardness.

Here, a method of forming an uneven surface on the resin layer is notparticularly limited. For example, the resin composition is cured whilea coating layer of the resin composition is in contact with a desiredmold having an uneven structure, or an uneven structure may beimplemented by mixing particles having suitable particle sizes with aresin composition, and coating and curing the mixture.

Also, the glariness preventing layer may be implemented using particleshaving a different refractive index from that of the resin layer.

In one embodiment, the particles may have a difference in refractiveindex with the resin layer of 0.03 or less or 0.02 to 0.2. When thedifference in refractive index is excessively small, it is difficult toinduce a haze, and when the difference in refractive index isexcessively large, scattering occurs a lot in the resin layer, andtherefore a haze is increased but a decrease in light transmittivity ora contrast characteristic may be induced. By considering these aspects,suitable particles may be selected.

A shape of the particle included in the resin layer may be, but is notparticularly limited to, for example, spherical, oval, polygonal,amorphous, or other shapes. The particle has an average diameter of 50to 5,000 nm. In one embodiment, as the particles, particles having anuneven surface may be used. Such particles may have, for example, anaverage surface roughness (Rz) of 10 to 50 nm or 20 to 40 nm, and/or themaximum height of a bump on the uneven surface of approximately 100 to500 nm or 200 to 400 nm, and a width between bumps of approximately 400to 1,200 nm or 600 to 1,000 nm. Such particles have excellentcompatibility with the resin layer or dispersibility in the resin layer.

As the particles, various inorganic or organic particles may be used.The inorganic particles may be silica, amorphous titania, amorphouszirconia, indium oxide, alumina, amorphous zinc oxide, amorphous ceriumoxide, barium oxide, calcium carbonate, amorphous barium titanate, orbarium sulfate, and the organic particles may be particles including acrosslinking product or non-crosslinking product of an organic materialsuch as an acryl resin, a styrene resin, an urethane resin, a melamineresin, a benzoguanamine resin, an epoxy resin, or a silicon resin, butthe present application is not limited thereto.

The uneven structure formed on the resin layer or the content of theparticles is not particularly limited. The shape of the uneven structureor the content of the particles may be controlled to have a haze of theresin layer of approximately 5 to 15%, 7 to 13%, or 10% for the AGlayer, or approximately 1 to 3% for the SG layer. The haze may bemeasured using a hazemeter such as HR-100 or IIM-150 commerciallyavailable from Sepung according to a manufacturer's manual.

The low reflection layer such as the AR or LR layer may be formed bycoating a low refractive material. Various low refractive materialscapable of forming the low reflection layer are known, and may besuitably selected and used for the optical device. The low reflectionlayer may be formed to have a reflectance of approximately 1% or less bycoating a low refractive material.

To form a surface treatment layer, a material disclosed in KoreanUnexamined Patent Application No. 2007-0101001, 2011-0095464,2011-0095004, 2011-0095820, 2000-0019116, 2000-0009647, 2000-0018983,2003-0068335, 2002-0066505, 2002-0008267, 2001-0111362, 2004-0083916,2004-0085484, 2008-0005722, 2008-0063107, 2008-0101801, or 2009-0049557may also be used.

One or a combination of at least two of the surface treatment layers maybe formed. The combination may be formed by forming a high hardnesslayer on a surface of a base layer, and forming a low reflection layerthereon.

In yet another aspect, the present application provides a displaydevice, for example, a liquid crystal display (LCD). The illustrativedisplay device may include a liquid crystal panel, and the opticaldevice may be adhered to one or both surfaces of the liquid crystalpanel. The film may be adhered to the liquid crystal panel using, forexample, an adhesive or a pressure-sensitive adhesive. Here, theadhesive or pressure-sensitive adhesive is one rather than apressure-sensitive adhesive present in the above-described protectivefilm.

A type of the liquid crystal panel included in the LCD is notparticularly limited. For example, the type of the liquid crystal panelis not limited, and all types of known liquid crystal panels including:all types of passive matrix panels including a twisted nematic(TN)-mode, super twisted nematic (STN)-mode, ferroelectric (F)-mode, andpolymer dispersed LCD (PD LCD)-mode panels; all types of active matrixpanels including a two terminal-mode and three terminal-mode panels; anIPS-mode panel; and a vertically aligned (VA)-mode panel, may beapplied. In addition, types of other components included in the LCD anda method of manufacturing the same are not particularly limited, either,and therefore general components known in the art may be employedwithout limitation.

Effect

A pressure-sensitive adhesive composition of the present application canexhibit excellent storage stability, suitable low speed and high speedpeel-off strengths after having a crosslinking structure, and anexcellent balance between them. Accordingly, the pressure-sensitiveadhesive composition can exhibit an excellent protective effect whenapplied to a protective film, can be easily peeled in a high speedpeel-off and thus advantageous for a high speed process, and can exhibitan excellent antistatic characteristic.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Hereinafter, a pressure-sensitive adhesive composition will be describedin detail with reference to examples and comparative examples, but thescope of the pressure-sensitive adhesive composition is not limited tothe following examples.

1. Measurement of Pot Life

A viscosity of a coating solution (pressure-sensitive adhesivecomposition) of each Example or Comparative Example prepared by mixing acrosslinking agent with a polymer which was previously prepared wasmeasured at 0 hr and 24 hr after the preparation, and then a pot lifewas evaluated according to the following criteria. Here, the viscositymay be measured in an RPM section in which a torque of a confidenceinterval was maintained using a Brookfield viscometer (DV-II+) byputting the coating solution into a 250 mL glass bottle to have a weightof approximately 200 g and keeping the bottle in a constant temperaturebath maintaining a temperature at 23° C. for 30 minutes to meet atemperature equilibrium.

<Criteria for Evaluating Pot Life>

A: At 24 hr after preparation (0 hr), change in viscosity was less than30%

B: At 24 hr after preparation (0 hr), change in viscosity was 30% ormore

2. Measurement of Low Speed Peel-Off Strength

A pressure-sensitive adhesive sheet prepared in Example or ComparativeExample was adhered to a glariness preventing layer formed on apolarizing plate using a 2 Kg roller according to JIS Z 0237. Afterward,the resulting product was maintained at 23° C. and a relative humidityof 65% for 24 hours, and cut to have a size of 25 mm×120 mm(width×length), thereby preparing a sample. Afterward, the sample wasfixed on a glass substrate, and then the pressure-sensitive adhesivesheet was peeled from the glariness preventing layer in a horizontaldirection at a peel-off angle of 180 degrees and a peel-off speed of 0.3m/min using a tensile tester to measure a peel-off strength. Thepeel-off strength was measured for two same samples, and an average wasadopted.

3. Measurement of High Speed Peel-Off Strength

A pressure-sensitive adhesive sheet prepared in Example or ComparativeExample was adhered to a glariness preventing layer formed on apolarizing plate using a 2 Kg roller according to JIS Z 0237. Afterward,the resulting product was maintained at 23° C. and a relative humidityof 65% for 24 hours, and cut to have a size of 25 mm×250 mm(width×length), thereby preparing a sample. Afterward, the sample wasfixed on a glass substrate, and then the pressure-sensitive adhesivesheet was peeled from the glariness preventing layer in a horizontaldirection at a peel-off angle of 180 degrees and a peel-off speed of 30m/min using a tensile tester to measure a peel-off strength. Thepeel-off strength was measured for two same samples, and an average wasadopted.

4. Measurement of Peel-Off Electrostatic Discharge (ESD)

A sample was prepared by the same method as described in themeasurements of low speed and high speed peel-off strengths, except thatthe sample had a size of approximately 22 cm×25 cm (width×length).Subsequently, the sample was fixed on a glass substrate, apressure-sensitive adhesive sheet of the sample was peeled using atensile tester at a peel-off angle of approximately 180 degrees and apeel-off speed of 40 m/min to measure peel-off ESD.

5. Staining after Removal of Pressure-Sensitive Adhesive Sheet

The pressure-sensitive adhesive sheet was peeled from the same sampleused in the measurement of the low speed peel-off strength, and stainingon a surface of an adherend due to static electricity was observed andevaluated according to the following criteria.

<Evaluation Criteria>

A: when staining was not observed on a surface of the adherend

B: when staining was observed on a surface of the adherend

Preparation Example 1. Preparation of Acrylic Polymer (A)

85 parts by weight of 2-ethylhexyl acrylate (2-EHA), 2 parts by weightof 4-hydroxybutyl acrylate (4-HBA), 5 parts by weight of 2-hydroxyethylacrylate (2-HEA), 3 parts by weight of dimethyl acrylamide, and 5 partsby weight of polyethyleneglycol monomethylether methacrylate(ethyleneoxide unit added mole ratio(number?): 9 mol) were added to an 1L reactor equipped with a cooling device to perform a reflux of anitrogen gas and facilitate control of a temperature, and then 100 partsby weight of ethyl acetate was added as a solvent. Subsequently, anitrogen gas was purged for 1 hour to remove oxygen, a reactioninitiator (AIBN: azobisisobutyronitrile) was added for a reaction forapproximately 8 hours, and the reaction product was diluted with ethylacetate. Therefore, an acrylic polymer (A) was prepared.

Preparation Examples 2 to 15. Preparation of Acrylic Polymers B to L

An acrylic polymer was prepared by the same method as described inExample 1, except that a ratio of monomers used to prepare the polymerwas changed as shown in Tables 1 and 2.

TABLE 1 Preparation Example 1 2 3 4 5 6 7 8 9 Polymer A B C D E F G H IEHA 85  72  85  73 98 79 83 88  77 BA — 5 8 5 HBA 2 2 2 3 1  2 2 2 HEA 510  3 4  2 5 15 5 10 DMAA 3 6 9 10 6 DAAA PEGMA 5 5 5 2 15 5 Contentunit: parts by weight Solid content unit: wt % Viscosity unit: cP EHA:2-ethylhexyl acrylate BA: butyl acrylate HBA: 4-hydroxybutyl acrylateHEA: 2-hydroxyethyl acrylate DMMA: dimethyl acrylamide DAAA: diacetoneacrylamide PEGMA: polyethyleneglycol monomethylether methacrylate(ethyleneoxide unit added mole number: 9 mol)

TABLE 2 Preparation Example 10 11 14 Polymer J K L EHA 63 63 84 BA 12 12HBA 6 3 HEA 6 2 DMAA 10 10 9 DAAA PEGMA 4 4 5 Content unit: parts byweight Solid content unit: wt % Viscosity unit: cP EHA: 2-ethylhexylacrylate BA: butyl acrylate HBA: 4-hydroxybutyl acrylate HEA:2-hydroxyethyl acrylate DMMA: dimethyl acrylamide DAAA: diacetoneacrylamide PEGMA: polyethyleneglycol monomethylether methacrylate(ethyleneoxide unit added mole number: 9 mol)

Example 1

Preparation of Pressure-Sensitive Adhesive Composition

A pressure-sensitive adhesive composition was prepared by uniformlymixing 5.0 parts by weight of a mixture (MHG-80B, Asahi Kasei ChemicalsCorporation (AKCC)) of an isophorone diisocyanate-based crosslinkingagent and a hexamethylene diisocyanate-based crosslinking agent as acrosslinking agent and 0.5 parts by weight of lithiumbis(trifluoromethanesulfonyl)imide) (LiTFSi) relative to 100 parts byweight of the acrylic polymer (A) of Preparation Example 1, and dilutingthe resulting mixture to have a suitable concentration in considerationof coatability.

Preparation of Pressure-Sensitive Adhesive Sheet

A uniform coating layer was formed to have a thickness of approximately20 μm by coating and drying the prepared pressure-sensitive adhesivecomposition on one surface of a poly(ethylene terephthalate) (PET) film(thickness: 38 μm). Subsequently, the coating layer was maintained atapproximately 90° C. for 3 minutes to induce a crosslinking reaction,thereby preparing a pressure-sensitive adhesive sheet.

Examples 2 to 4 and Comparative Examples 1 to 8

Pressure-sensitive adhesive compositions were prepared by the samemethod as described in Example 1, except that component ratios of therespective pressure-sensitive adhesive composition were changed as shownin Tables 3 and 4.

TABLE 3 Example 1 2 3 4 Polymer Type A B C D Ratio 100 100 100 100Crosslinking agent Ratio 5 6 5 6 Li salt Ratio 0.5 0.5 0.5 0.5 Ratiounit: parts by weight Type of Crosslinking agent: mixture of isophoronediisocyanate-based crosslinking agent and hexamethylenediisocyanate-based crosslinking agent (MHG-80B, AKCC) Type of Li salt:lithium bis(trifluoromethanesulfonyl)imide (LiTFSi)

TABLE 4 Comparative Example 1 2 3 4 5 6 7 8 Polymer Type E F G H I J K LRatio 100 100 100 100 100 100 100 100 Cross- Ratio 5 5.5 7 5 6 6 6 5linking agent Li salt Ratio 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Ratio unit:parts by weight Type of Crosslinking agent: mixture of isophoronediisocyanate-based crosslinking agent and hexamethylenediisocyanate-based crosslinking agent (MHG-80B, AKCC) Type of Li salt:lithium bis(trifluoromethanesulfonyl)imide (LiTFSi)

Physical properties were evaluated with respect to thepressure-sensitive adhesive compositions of Examples and ComparativeExamples, and summarized in Tables 5 and 6.

TABLE 5 Example 1 2 3 4 Pot life A A A A L-peel(unit: gf/25 mm) 5.3 95.5 11 H-peel(unit: gf/25 mm) 130 200 130 180 ESD(unit: kV) 0.15 0.20.15 0.3 Staining evaluation A A A A L-peel: low speed peel-off strengthH-peel: high speed peel-off strength

TABLE 6 Comparative Example 1 2 3 4 5 6 7 8 Pot life A B B A A A A AL-peel 2.3 2.7 7 2 5.5 6.3 1.5 1.9 H-peel 100 110 210 120 210 220 50 70ESD 0.7 0.3 0.45 0.9 0.3 0.15 0.2 0.2 Staining B A B B A A A A L-peel:low speed peel-off strength H-peel: high speed peel-off strengthESD(unit: kV)

What is claimed is:
 1. A surface protective film comprising: a surfaceprotective base layer; and a pressure-sensitive adhesive layer formed onone or both surfaces of the surface protective base layer, wherein thepressure-sensitive adhesive layer has a ratio (H/L) of a high speedpeel-off strength (H) to a low speed peel-off strength (L) of 1 to 25,wherein the low speed peel-off strength (L) is measured at a peelingangle of 180 degrees and a peeling speed of 0.3 m/min with respect to anadherend having a surface energy of 30 mN/m or less and the high speedpeel-off strength (H) is measured at a peeling angle of 180 degrees anda peeling speed of 30 m/min with respect to an adherend having a surfaceenergy of 30 mN/m or less, wherein the pressure-sensitive adhesive layercomprises a pressure-sensitive adhesive composition in a crosslinkedstate, and the pressure-sensitive adhesive composition comprises: apolymer comprising a polymerization unit of a monomer of Formula 1, apolymerization unit of a nitrogen-containing monomer, a polymerizationunit of a first monomer represented by Formula 2, in which alkylenegroups of A and B of Formula 2 have 1 to 3 carbon atoms, and apolymerization unit of a second monomer represented by Formula 2, inwhich alkylene groups of A and B of Formula 2 have 4 to 8 carbon atoms,in which a ratio (A/B) of a weight (A) of the polymerization unit of thefirst monomer and a weight (B) of the polymerization unit of the secondmonomer is more than 1 and not more than 5; and an ionic compound:

where Q is hydrogen or an alkyl group, U is an alkylene group, Z ishydrogen, an alkyl group, or an aryl group, m is a number of 1 to 20, Aand B are each independently an alkylene group, and n is
 0. 2. Thesurface protective film according to claim 1, wherein thenitrogen-containing monomer is dialkyl (meth)acrylamide.
 3. The surfaceprotective film according to claim 1, wherein the polymer comprises apolymerization units of 0.1 to 6.0 parts by weight of the monomer ofFormula 1, 1 to 30 parts by weight of the nitrogen-containing monomer,0.1 to 15 parts by weight of the first monomer and 0.1 to 5 parts byweight of the second monomer.
 4. The surface protective film accordingto claim 1, wherein the pressure-sensitive adhesive composition furthercomprises a compound of Formula 3:

where M₁ to M₅ are each independently R¹—N, (R²)(R³)—C, or (R⁴)(R⁵)—C,in which R¹ is a hydrogen atom, an alkyl group, or an alkoxy group, R²and R³ are each independently an alkyl group, R⁴ and R⁵ are eachindependently a hydrogen atom or an alkyl group, L is an alkylene groupor an alkylidene group, P is an alkyl group or a substituent of Formula4, at least one of M₂ to M₄ is R¹—N, and M₁, M₂, M₃, M₄, or M₅ justadjacent to M₂, M₃, or M₄ that is R¹—N is (R²)(R³)—C, and

where M₆ to M₁₀ are each independently R¹—N, (R²)(R³)—C, or (R⁴)(R⁵)—C,in which R¹ is a hydrogen atom, an alkyl group, or an alkoxy group, R²and R³ are each independently an alkyl group, and R⁴ and R⁵ are eachindependently a hydrogen atom or an alkyl group, at least one of M₇ toM₉ is R¹—N, and M₆, M₇, M₈, M₉, or M₁₀ just adjacent to M₇, M₈, or M₉that is R¹—N is (R²)(R³)—C, wherein in Formulas 3 and 4, the N atom orthe C atom in R¹—N, (R²)(R³)—C, or (R⁴)(R⁵)—C is present at the positionof M₁ to M₁₀, and a substituent selected from R¹ to R⁵ binds to the Natom or the C atom.
 5. The surface protective film according to claim 4,wherein, in Formula 3, R¹ is a hydrogen atom, an alkyl group having 1 to8 carbon atoms, or an alkoxy group having 4 to 16 carbon atoms, R² andR³ are each independently an alkyl group having 1 to 12 carbon atoms,and L is an alkylene group having 4 to 12 carbon atoms or an alkylidenegroup having 2 to 10 carbon atoms.
 6. The surface protective filmaccording to claim 4, wherein the compound of Formula 3 isbis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, methyl1,2,2,6,6-pentamethyl-4-piperidyl sebacate, propanedioic acid2-[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]-2-butyl-1,3-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)ester, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, orbis-(1-octyloxy-2,2,6,6-tetramethyl-4-piperidinyl)sebacate.
 7. Thesurface protective film according to claim 4, wherein the compound ofFormula 3 is comprised in the pressure-sensitive adhesive composition at0.01 to 10 parts by weight relative to 100 parts by weight of thepolymer.
 8. The surface protective film according to claim 1, whereinthe pressure-sensitive adhesive composition further comprises analiphatic isocyanate crosslinking agent.
 9. The surface protective filmaccording to claim 8, wherein the crosslinking agent is comprised in thepressure-sensitive adhesive composition at 0.01 to 10 parts by weightrelative to 100 parts by weight of the polymer.
 10. The surfaceprotective film according to claim 8, wherein the crosslinking agentcomprises at least one selected from the group consisting of analiphatic cyclic isocyanate compound and an aliphatic non-cyclicisocyanate compound.
 11. The surface protective film according to claim10, wherein the aliphatic cyclic isocyanate compound is an isocyanatecompound selected from isophorone diisocyanate, methylene dicyclohexyldiisocyanate, and cyclohexane diisocyanate, a dimer or trimer of theisocyanate compound, or a reaction product of the isocyanate compoundwith a polyol.
 12. The surface protective film according to claim 10,wherein the aliphatic non-cyclic isocyanate compound is an alkylenediisocyanate compound having 1 to 20 carbon atoms; a dimer or trimer ofan isocyanate compound; or a reaction product of the isocyanate compoundand a polyol.
 13. The surface protective film according to claim 1,wherein the low speed peel-off strength (L) is 1 to 40 gf/25 mm.
 14. Thesurface protective film according to claim 1, wherein the high speedpeel-off strength (H) is 10 to 300 gf/25 mm.
 15. The surface protectivefilm of claim 1, wherein the surface protective film is detachablyattached on a surface to be protected.
 16. An optical device in whichthe surface protective film of claim 1 is adhered to a surface thereofto be peeled.
 17. The optical device according to claim 16, wherein thesurface to which the protective film is adhered has a surface energy of30 mN/m or less.
 18. A display device, comprising the optical device ofclaim 16.